(1) Field of the Invention
The present invention relates to a data communication system, and to a data transmitting apparatus and data receiving apparatus, where simulated bidirectional communication processing is performed between a data transmitting apparatus and a data receiving apparatus using one-way communication, such as a television (TV) broadcast.
(2) Description of the Prior Art
It is now possible to connect personal computers in the home to networks using a standard telephone line and so receive a great variety of information provided by servers around the world. The most representative example of such a network is the World Wide Web (WWW) on the Internet. WWW servers transmit a combination of image information and control information, which has the image information displayed within text information, to personal computers as the data for displaying a one-page image on the personal computer's screen. When such pages are made up of text information alone, only control information for displaying this text information is transmitted. This control information is written using HTML (HyperText Markup Language), with browser software executed by the personal computer decoding and executing the HTML code to display each page on the WWW which is downloaded by the user. Here, information indicating a link to another page can be attached to character strings and images in a page, so that when the user makes a selection operation for such a character string or image using a mouse, for example, the browser will access the WWW server that provides the indicated page and will obtain the information for displaying this new page. On obtaining this information, the browser will decode and execute its content to display the new page.
Japanese Laid-Open Patent Application 7-322226 (1995) discloses a method for multiplexing control information that can generate the kind of interactive display described above into a TV broadcast which is transmitted using a TV broadcast ground wave. In this method, the program transmitting apparatus multiplexes data, written in a language which resembles HTML for composing an interactive screen, into a program broadcast before transmitting. On receiving this broadcast, the program receiving apparatus interprets the composition of the interactive screen and combines basic display elements which have been stored inside its construction in accordance with the indicated composition to display the interactive screen.
The above method has a major drawback in that the control information is written in a language for indicating a variety of control operations which are performed for display, so that the receiving apparatus needs to interpret and execute these control operations one by one to perform display. Additionally, most high resolution images provided by WWW servers are compressed using complex techniques, so that when a receiving apparatus attempts to display such image information, it is usually necessary to perform decompression in addition to the processes for display in accordance with the control information. Since such complex processing is required, the load of the receiving apparatus is considerable, which greatly increases the cost of the necessary hardware for the receiving apparatus. This problem makes this communication method unsuitable for a TV broadcast communication system in which transmission is performed from a small number of transmitting apparatuses to a large number of receiving apparatuses.